Coupler

ABSTRACT

The present invention provides a coupler having a high degree of coupling. The coupler comprises first and second dielectric substrates each having first and second surfaces which are parallel to each other. A ground conductor is formed on the first surface of the first dielectric substrate, and two coupling line conductors and are formed on the second surface of the second dielectric substrate close to each other so as to be electromagnetically coupled to each other. Via conductors and are filled in through holes passing through the second dielectric substrate, and are placed and connected to the two coupling line conductors so as to enhance the degree of electromagnetic coupling, thereby increasing the opposing areas between the coupling line conductors to increase the capacitance.

TECHNICAL FIELD

The present invention relates to couplers. More specifically, thisinvention relates to directional couplers in microwave circuits orcouplers to be used for filters and, more particularly, to couplerswhich provide high degrees of coupling in cases of using striplines.

BACKGROUND ART

Conventionally, couplers have been used for various microwave circuits,such as filter circuits, balanced amplifiers, balanced mixer, andbaluns.

FIGS. 6( a) through 6(g) are diagrams showing a coupler that employsconventional ¼-wavelength end short-circuited type coupling lines.

FIG. 6( c) is a top plan view showing a conventional coupler, in whichparts that are not seen from the top are indicated by dashed lines. FIG.6( a) is a longitudinal sectional view of the coupler along line A9–A10of FIG. 6( c). FIG. 6( b) is a longitudinal sectional view thereof alongline A11–A12 of FIG. 6( c). FIG. 6( d) is a transverse sectional viewthereof along line A1–A2 of FIG. 6( c). FIG. 6( e) is a transversesectional view thereof along line A3–A4 of FIG. 6( c). FIG. 6( f) is atransverse sectional view thereof along line A5–A6 of FIG. 6( c). FIG.6( g) is a transverse sectional view thereof along line A7–A8 of FIG. 6(c).

As shown in FIGS. 6( a) and 6(b), the conventional coupler includes aground conductor 603 that is formed on an under surface of a firstdielectric substrate 601, and a ground conductor 604 that is formed on atop surface of a second dielectric substrate 602.

Further, as shown in FIGS. 6( e) and 6(f), between the first dielectricsubstrate 601 and the second dielectric substrate 602, there are formedsignal input/output line conductors 612 and 613 that employ striplines,and two coupling line conductors 620 and 621 that are adjacent to eachother so as to be electromagnetically coupled, in symmetry with respectto the center line of the ground conductor 604.

In addition, via conductors 630, 631, 632 and 633 are filled in throughholes that pass through the first dielectric substrate 601 and thesecond dielectric substrate 602.

As shown in FIGS. 6( a) and 6(b), the via conductors 630, 631 and thevia conductors 632, 633 short-circuit not-opposing end portions of thecoupling line conductors 620 and 621 to the ground conductors 604 and603 at a position of line A7–A8 of FIG. 6( c) and at a position of lineA1–A2 of FIG. 6( c), respectively, thereby providing inter-digitalcoupling.

Further, on the side surfaces of the first dielectric substrate 601 andthe second dielectric substrate 602, ground conductors 605, 606, 607,and 608 are formed.

As described above, the conventional coupler utilizing the ¼-wavelengthend short-circuited type coupling lines is formed using the striplines,with the coupling line conductors 620 and 621 being enclosed with theground conductors 603, 604, 605, 606, 607, and 608.

The conventional coupler utilizing the ¼-wavelength end short-circuitedtype coupling lines connects the signal input/output line conductors 612and 613 to the coupling line conductors 620 and 621 symmetrically withrespect to a point in such a manner that the conductors 612 and 613 arenot opposing to each other, and an input/output impedance is decidedfrom a distance from the connecting point to the end of the couplingline conductor 620 or 621.

Signal input/output end face electrodes 610 and 611 at the mounting on aprinted circuit board are formed on the side surfaces of the firstdielectric substrate 601 and the second dielectric substrate 602, andare connected to the signal input/output line conductors 612 and 613,respectively.

Here, the coupling line conductors 620 and 621 each have a length alongthe length, corresponding to a ¼ wavelength, i.e., a longitudinal lengthcorresponding to ¼ λg (λg is an intra-tube wavelength).

When an analysis is performed on the conventional coupler utilizing the¼-wavelength end short-circuited type coupling lines, using quasi-TEMapproximation based on a known even/odd orthogonal mode excitationmethod (J. Reed) or using an analyzing method in an even or odd mode,which is disclosed by “Practical Use, Lectures on microwavetechnology—Theory and Fact—Volume 3, June 2001 (written by YoshihiroKonishi, published by K-Laboratory)”, in-phase excitation occurs in theeven mode while opposite-phase excitation occurs in the odd mode.

In this case, characteristic impedances Zodd and Zeven of couplingtransmission lines of the coupling lines in the odd and even modes arerepresented by [Formula 1] and [Formula 2].

[Formula 1]Zodd=1/(Vp×(C1+2×C12))[Ω][Formula 2]Zeven=1/(Vp×C1)[Ω]

Here, Vp is a speed at which the electromagnetic field propagatesthrough a transmission line. C1 is a capacitance per unit length betweenthe coupling line conductors 620 and 621 (striplines) and the groundconductors 603 and 604, and C12 is a capacitance per unit line betweenthe coupling line conductors 620 and 621.

The degree K of coupling of the conventional coupler that utilizes the¼-wavelength end short-circuited type coupling lines can be expressed bya following formula, using the characteristic impedances Zodd and Zeven.

[Formula 3]K=20 log {(Zeven−Zodd)/(√2×(Zeven+Zodd))[dB]

By substituting [Formula 1] and [Formula 2] into [Formula 3], following[Formula 4] indicating the coupling degree K is obtained.

[Formula 4]K=20 log {C12/(√2×(C1+C12))}

Thus, the coupling degree K of the conventional coupler that utilizesthe ¼-wavelength end short-circuited coupling line is represented asdescribed above.

However, in the above-mentioned conventional coupler utilizing thestriplines, it is possible to increase the coupling degree K only byextremely reducing the spacing between two coupling line conductors 620and 621. But, the minimum spacing between the two coupling lineconductors 620 and 621 is limited from the viewpoint of manufacturing.

Recently, a low-temperature co-fired ceramic (LTCC) has been developed,whereby it has become possible to thin an insulating layer andminiaturize the coupler. However, when the insulating layer is thinned,the capacitance C1 per unit length between the coupling line conductors620 and 621 as the striplines, and the ground conductors 603 and 604 isincreased. Accordingly, the coupling degree K of the coupling line isfurther reduced as expressed by [Formula 4].

To solve this problem, Japanese Patent Application No. Hei. 05-135749(Japanese Published Patent Application No. Hei. 06-350313) suggests a¼-wavelength coupling line type directional coupler which is obtained byimproving the above-mentioned conventional coupler.

The prior art as disclosed in this publication relates to lineconductors mainly using microstrips, but it is easily affected byelectromagnetic interference from outside, and further, componentscannot be placed above or below the ¼-wavelength coupling linedirectional coupler, so that it is not suitable for high-densitypackaging and cannot be miniaturized.

The present invention is made to overcome the above-mentionedconventional problems, and has for its object to provide a couplerhaving a higher coupling degree K, which is smaller in size and allowshigher-density packaging with relative to the prior art.

SUMMARY OF THE INVENTION

To overcome the conventional problems, according to a first aspect ofthe present invention, there is provided a coupler comprising: a firstdielectric substrate having a first surface and a second surface whichare parallel to each other; a second dielectric substrate having a firstsurface and a second surface which are parallel to each other, thesecond dielectric substrate being placed on the second surface of thefirst dielectric substrate; a ground conductor that is formed on thefirst surface of the first dielectric substrate; two coupling lineconductors each having a length of a ¼ wavelength, the coupling lineconductors being close to each other on the second surface of the seconddielectric substrate so as to be electromagnetically coupled to eachother; and plural via conductors which are filled in plural throughholes passing through the second dielectric substrate and are placed andconnected to the two coupling line conductors.

According to the present invention, the opposing areas between thecoupling line conductors are increased in the odd mode by an amount thatis larger than an increase in the capacitance between the coupling lineconductor and the ground conductor in the even mode, thereby increasingthe degree of coupling of the coupler.

According to a second aspect of the present invention, in the coupler asdefined in the first aspect, a third dielectric substrate having a firstsurface and a second surface which are parallel to each other is formedon the second surface of the second dielectric substrate, and a groundconductor is formed on the second surface of the third dielectricsubstrate.

According to the present invention, as the coupler is enclosed with theground conductors, the coupler has resistance to electromagneticinterference from outside, whereby it is possible to place thecomponents at high densities, resulting in a miniaturized apparatus.

According to a third aspect of the present invention, in the coupler asdescribed in the first aspect, via conductors that are filled in throughholes passing from the first dielectric substrate to the seconddielectric substrate are provided, and the via conductors that arefilled in the through holes passing through the two substratesshort-circuit ends of the two coupling line conductors, which are notopposing to each other, to the ground conductor that is formed on thefirst surface of the first dielectric substrate, thereby providinginter-digital coupling.

According to the present invention, it is possible to form aninter-digital filter.

According to a fourth aspect of the present invention, in the coupler asdescribed in the second aspect, via conductors that are filled inthrough holes passing from the first dielectric substrate to the thirddielectric substrate are provided, and the via conductors that arefilled in the through holes passing through the three substratesshort-circuit ends of the two coupling line conductors, which are notopposing to each other, to the ground substrates that are formed on thefirst surface of the first dielectric substrate and the second surfaceof the third dielectric substrate, thereby providing inter-digitalcoupling.

According to the present invention, it is possible to form aninter-digital filter.

According to a fifth aspect of the present invention, in the coupler asdescribed in the third or fourth aspects, the via conductors that arefilled in the through holes passing through the two or three substratesshort-circuit opposing ends of the two coupling line conductors to theground conductor that is formed on the first surface of the firstdielectric substrate, or to the ground conductors that are formed on thefirst surface of the first dielectric substrate and the second surfaceof the third dielectric substrate, thereby providing comb-line coupling.

According to the present invention, it is possible to form a comb-linefilter.

According to a sixth aspect of the present invention, in the coupler asdescribed in any of aspects 3 to 5, the plural via conductors that arefilled in the plural through holes passing through the second dielectricsubstrate are placed and connected to the two coupling line conductorsat regular intervals.

According to the present invention, it is possible to place the viaconductors uniformly at high densities.

According to a seventh aspect of the present invention, in the coupleras described in any of aspects 3 to 5, the plural via conductors thatare filled in the plural through holes passing through the seconddielectric substrate are placed and connected to the two coupling lineconductors in a straight line along the length.

According to the present invention, it is possible to place the viaconductors on the coupling line conductors uniformly at high densities.

According to an eighth aspect of the present invention, in the coupleras described in any of aspects 3 to 5, the plural via conductors thatare filled in the plural through holes passing through the seconddielectric substrate are placed and connected to the opposing twocoupling line conductors, respectively, on a part which is closer to aline intermediate between the two coupling line conductors.

According to the present invention, it is possible to obtain a higherdegree of coupling by placing the opposing many high-density viaconductors as close as possible to each other.

According to a ninth aspect of the present invention, in the coupler asdescribed in any of aspects 3 to 5, the plural via conductors that arefilled in the plural through holes passing through the second dielectricsubstrate are placed and connected to the opposing two coupling lineconductors, respectively, on a part which is closer to a lineintermediate between the two coupling line conductors at regularintervals in a straight line along the length.

According to the present invention, it is possible to obtain a higherdegree of coupling by placing the opposing many high-density viaconductors as close as possible to each other.

According to aspect 10 of the present invention, in the coupler asdescribed in any of aspects 3 to 5, the plural via conductors that arefilled in the plural through holes passing through the second dielectricsubstrate are placed and connected to the two coupling line conductorsso as to form thin parts and dense parts.

According to the present invention, it is possible to place the viaconductors on parts of the coupling line conductors at high densities.

According to aspect 11 of the present invention, in the coupler asdescribed in any of aspects 3 to 5, the plural via conductors that arefilled in the plural through holes passing through the second dielectricsubstrate are placed and connected to the two coupling line conductorsin such a manner that dense parts each being composed of a group of thevia conductors are placed intermittently.

According to the present invention, the opposing areas between thecoupling line conductors are increased in the odd mode by an amount thatis larger than an increase of the capacitance between the coupling lineconductor and the ground conductor in the even mode, thereby increasingthe degree of coupling of the coupler.

According to aspect 12 of the present invention, in the coupler asdefined in aspect 11, the plural via conductors that are filled in theplural through holes passing through the second dielectric substrate areplaced and connected to the opposing two coupling line conductors,respectively, on a part which is closer to a line intermediate betweenthe two coupling line conductors in a straight line along the length.

According to the present invention, it is possible to obtain a higherdegree of coupling by placing the opposing many high-density viaconductors as close as possible to each other.

According to aspect 13 of the present invention, in the coupler asdescribed in any of aspects 3 to 5, the plural via conductors that arefilled in the plural through holes passing through the second dielectricsubstrate are placed and connected to the two coupling line conductorsin a zigzag manner so that the via conductors are opposing to eachother.

According to the present invention, it is possible to enlarge thespacing between the via conductors and, especially in LTCC, it ispossible to avoid cracks due to a warp that occurs in the dielectricsubstrate as an insulator. Further, the opposing areas between thecoupling line conductors are increased in the odd mode by an amount thatis larger than an increase in the capacitance between the coupling lineconductor and the ground conductor in the even mode, thereby increasingthe degree of coupling of the coupler.

According to aspect 14 of the present invention, in the coupler asdescribed in any of aspects 3 to 5, the plural via conductors that arefilled in the plural through holes passing through the second dielectricsubstrate are placed and connected to the two coupling line conductorsin a staggered manner so that the via conductors are opposing eachother.

According to the present invention, it is possible to enlarge thespacing between the via conductors and, especially in LTCC, it ispossible to avoid cracks due to a warp that occurs in the dielectricsubstrate as an insulator. Further, the opposing areas between thecoupling line conductors are increased in an odd mode by an amount thatis larger than an increase in the capacitance between the coupling lineconductor and the ground conductor in the even mode, thereby increasingthe degree of coupling of the coupler.

According to aspect 15 of the present invention, in the coupler asdescribed in any of aspects 3 to 5, two second line conductors arefurther provided between the second surface of the first dielectricsubstrate and the first surface of the second dielectric substrate, andthe two coupling line conductors and the two second line conductors areconducting individually, and plural via conductors that are filled inthe plural through holes passing through the second dielectric substrateare sandwiched between and connected to the coupling line conductor andthe second line conductor, respectively.

According to the present invention, it is possible to enlarge thespacing between the via conductors, thereby increasing the couplingdegree K of the coupling line. When this coupler is employed for aband-pass filter, it is possible to increase the passband, and realize ahigh-density packaging of multiple layers.

According to aspect 16 of the present invention, in the coupler asdescribed in aspect 9, two second line conductors are further providedbetween the second surface of the first dielectric substrate and thefirst surface of the second dielectric substrate, and the two couplingline conductors and the two second line conductors are conductingindividually. Plural via conductors that are filled in the pluralthrough holes passing through the second dielectric substrate aresandwiched between and connected to the coupling line conductor and thesecond line conductor, respectively.

According to the present invention, it is possible to enlarge thespacing between the via conductors, thereby increasing the couplingdegree K of the coupling line. When this coupler is employed for aband-pass filter, it is possible to increase the passband, and realize ahigh-density packaging of multiple layers.

According to aspect 17 of the present invention, there is provided acoupler comprising: a first dielectric substrate having a first surfaceand a second surface which are parallel to each other; a seconddielectric substrate having a first surface and a second surface whichare parallel to each other, the second dielectric substrate being placedon the second surface of the first dielectric substrate; a thirddielectric substrate having a first surface and a second surface whichare parallel to each other, the third dielectric substrate being placedon the second surface of the second dielectric substrate; a groundconductor which is formed on the first surface of the first dielectricsubstrate; two coupling line conductors each having a length of a ¼wavelength, the coupling line conductors being close to each other onthe second surface of the second dielectric substrate so as to beelectromagnetically coupled to each other; and plural via conductorswhich are filled in plural through holes passing through the seconddielectric substrate or the third dielectric substrate, and placed andconnected to the two coupling line conductors.

According to the present invention, the opposing areas between thecoupling line conductors are increased in the odd mode by an amount thatis larger than an increase in the capacitance between the coupling lineconductor and the ground conductor in the even mode, thereby increasingthe coupling degree of the coupler.

According to aspect 18 of the present invention, in the coupler asdescribed in aspect 17, a fourth dielectric substrate having a firstsurface and a second surface which are parallel to each other is formedon the second surface of the third dielectric substrate, and a groundconductor is formed on the second surface of the fourth dielectricsubstrate.

According to the present invention, the coupler has resistance toelectromagnetic interference from outside by enclosing the coupler withthe ground conductors, whereby it is possible to place the components athigh densities, resulting in a miniaturized apparatus.

According to aspect 19 of the present invention, in the coupler asdescribed in aspect 17, via conductors that are filled in through holespassing from the first dielectric substrate to the third dielectricsubstrate are provided, and the via conductors that are filled in thethrough holes passing through the three substrates short-circuit ends ofthe two coupling line conductors, which are not opposing each other, tothe ground conductor that is formed on the first surface of the firstdielectric substrate, thereby providing inter-digital coupling.

According to the present invention, it is possible to form aninter-digital filter.

According to aspect 20 of the present invention, in the coupler asdescribed in aspect 18, via conductors that are filled in the throughholes passing from the first dielectric substrate to the fourthdielectric substrate are provided, and the via conductors that arefilled in the through holes passing through the four substratesshort-circuit ends of the two coupling line conductors, which are notopposing each other, to the ground conductors that are formed on thefirst surface of the first dielectric substrate and the second surfaceof the fourth dielectric substrate, thereby providing inter-digitalcoupling.

According to the present invention, it is possible to form aninter-digital filter.

According to aspect 21 of the present invention, in the coupler asdescribed in aspect 19 or 20, the via conductors that filled in thethrough holes passing through the three or four substrates short-circuitopposing ends of the two coupling line conductors to the groundconductor that is formed on the first surface of the first dielectricsubstrate, or to the ground conductors that are formed on the firstsurface of the first dielectric conductor and the second surface of thefourth dielectric substrate, thereby providing comb-line coupling.

According to the present invention, it is possible to form a comb-linefilter.

According to aspect 22 of the present invention, in the coupler asdescribed in any of aspects 19 to 21, the plural via conductors filledin the plural through holes passing through the second or thirddielectric substrate are via conductors filled in the second dielectricsubstrate and via conductors filled in the third dielectric substrate,which are alternately placed and connected.

According to the present invention, it is possible to enlarge thespacing between the via conductors.

According to aspect 23 of the present invention, in the coupler asdescribed in aspect 22, the plural via conductors that are filled in theplural through holes passing through the second or third dielectricsubstrate are placed and connected to the opposing two coupling lineconductors, respectively, on a part that is closer to a lineintermediate between the two coupling line conductors at regularintervals in a straight line along the length.

According to the present invention, it is possible to enlarge thespacing between the via conductors, and when the via conductors areplaced in a long line at high densities, it is possible to avoid cracksdue to a warp that occurs in the dielectric substrate as an insulator,especially in LTCC. Further, the opposing areas between the couplingline conductors are increased in the odd mode by an amount that islarger than an increase in the capacitance between the coupling lineconductor and the ground conductor in the even mode, thereby increasingthe coupling degree of the coupler.

According to aspect 24 of the present invention, in the coupler asdescribed in any of aspects 9, 11, 14, 16, and 23, the coupler isemployed as a filter.

According to the present invention, when this coupler is employed for aband-pass filter, it is possible to enlarge the width of the passband,and realize a high-density packaging of multiple layers.

According to aspect 25 of the present invention, there is provided acoupler comprising: a first dielectric substrate having a first surfaceand a second surface which are parallel to each other; a groundconductor which is formed on the first surface of the first dielectricsubstrate; two coupling line conductors each having a length of a ¼wavelength, the coupling line conductors being close to each other onthe second surface of the first dielectric substrate so as to beelectromagnetically coupled to each other; and plural via dielectricsthat are dielectrics having permittivities lower than that of the firstdielectric substrate and being filled in plural through holes passingthrough the first dielectric substrate, and are placed and connected tothe two coupling line conductors.

According to the present invention, it is possible to enhance thecoupling degree of the coupling lines and, when this coupler is employedfor a band-pass filter, it is possible to enlarge the passband, therebyrealizing a high-density packaging of multiple layers.

According to aspect 26 of the present invention, in the coupler asdescribed in aspect 25, a second dielectric substrate having a firstsurface and a second surface which are parallel to each other is formedon the second surface of the first dielectric substrate, and a groundconductor is formed on the second surface of the second dielectricsubstrate.

According to the present invention, the coupler has resistance toelectromagnetic interference from outside by enclosing the coupler withthe ground conductor, and it is possible to place the components at highdensities, resulting in a miniaturized coupler.

According to aspect 27 of the present invention, in the coupler asdescribed in aspect 26, plural via dielectrics that are dielectricshaving permittivities lower than that of the second dielectric substrateand being filled in plural through holes passing through the seconddielectric substrate are placed and connected to the two coupling lineconductors.

According to the present invention, it is possible to increase thecoupling degree of the coupling line and, when this coupler is employedfor a band-pass filter, it is possible to enlarge the passband andrealize a high-density packaging of multiple layers.

According to aspect 28 of the present invention, in the coupler asdescribed in aspect 25, via conductors that are filled in through holespassing through the first dielectric substrate are provided, and the viaconductors that are filled in the through holes passing through thesubstrate short-circuit ends of the two coupling line conductors, whichare not opposing to each other, to the ground conductor that is formedon the first surface of the first dielectric substrate, therebyproviding inter-digital coupling.

According to the present invention, it is possible to form aninter-digital filter.

According to aspect 29 of the present invention, in the coupler asdescribed in aspect 27, via conductors that are filled in through holespassing through the first and second dielectric substrates are provided,and the via conductors that are filled in the through holes passingthrough the two substrates short-circuit ends of the two coupling lineconductors, which are not opposing to each other, to the groundconductors that are formed on the first surface of the first dielectricsubstrate and the second surface of the second dielectric substrate,thereby providing inter-digital coupling.

According to the present invention, it is possible to form aninter-digital filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a)–1(g) are diagrams illustrating a coupler according to afirst embodiment of the present invention, including longitudinalsectional views thereof (FIGS. 1( a) and 1(b)), a top plan view thereof(FIG. 1( c)), and transverse sectional views thereof (FIGS. 1( d), 1(e),1(f), and 1(g)).

FIGS. 2( a)–2(g) are diagrams illustrating a coupler according to asecond embodiment of the present invention, including longitudinalsectional views thereof (FIGS. 2( a) and 2(b)), a top plan view thereof(FIG. 2( c)), and transverse sectional views thereof (FIGS. 2( d), 2(e),2(f), and 2(g)).

FIGS. 3( a)–3(g) are diagrams illustrating a coupler according to athird embodiment of the present invention, including longitudinalsectional views thereof (FIGS. 3( a) and 3(b)), a top plan view thereof(FIG. 3( c)), and transverse sectional views thereof (FIGS. 3( d), 3(e),3(f), and 3(g)).

FIGS. 4( a)–4(g) are diagrams illustrating a coupler according to afourth embodiment of the present invention, including longitudinalsectional views thereof (FIGS. 4( a) and 4(b)), a top plan view thereof(FIG. 4( c)), and transverse sectional views thereof (FIGS. 4( d), 4(e),4(f), and 4(g)).

FIGS. 5( a)–5(g) are diagrams illustrating a coupler according to afifth embodiment of the present invention, including longitudinalsectional views thereof (FIGS. 5( a) and 5(b)), a top plan view thereof(FIG. 5( c)), and transverse sectional views thereof (FIGS. 5( d), 5(e),5(f), and 5(g)).

FIGS. 6( a)–6(g) are diagrams illustrating a conventional coupler,including longitudinal sectional views thereof (FIGS. 6( a) and 6(b)), atop plan view thereof (FIG. 6( c)), and transverse sectional viewsthereof (FIGS. 6( d), 6(e), 6(f), and 6(g)).

FIGS. 7( a)–7(f) are diagrams illustrating a coupler according to asixth embodiment of the present invention, including longitudinalsectional views thereof (FIGS. 7( a)), a top plan view thereof (FIG. 7(b)), and transverse sectional views thereof (FIGS. 7( c), 7(d), 7(e),and 7(f)).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

EMBODIMENT 1

FIGS. 1( a)–1(g) are diagrams illustrating a coupler that utilizes¼-wavelength end short-circuited type coupling lines according to afirst embodiment of the present invention.

FIG. 1( c) is a top plan view of the coupler according to the firstembodiment, in which parts that are not seen from the top are indicatedby dashed lines. FIG. 1( a) is a longitudinal sectional view of thecoupler along line A9–A10 of FIG. 1( c), and FIG. 1( b) is alongitudinal sectional view thereof along line A11–A12 of FIG. 1( c).FIG. 1( d) is a transverse sectional view of the coupler along lineA1–A2 of FIG. 1( c), FIG. 1( e) is a transverse sectional view thereofalong line A3–A4 of FIG. 1( c), FIG. 1( f) is a transverse sectionalview thereof along line A5–A6 of FIG. 1( c), and FIG. 1( g) is atransverse sectional view thereof along line A7–A8 of FIG. 1( c).

As shown in FIGS. 1( a) and 1(b), first, second and third dielectricsubstrates 141, 142 and 143 each have a first surface (under surface)and a second surface (top surface) which are parallel to each other. Thecoupler according to the first embodiment has a ground conductor 103which is formed on the under surface of the first dielectric substrate141, and a ground conductor 104 which is formed on the top surface ofthe third dielectric substrate 143.

Further, as shown in FIGS. 1( e) and 1(f), between the under surface ofthe third dielectric substrate 143 and the top surface of the seconddielectric substrate 142, there are formed signal input/output lineconductors 112 and 113 that employ striplines, and two coupling lineconductors 120 and 121 which are formed closely to each other so as tobe electromagnetically coupled with each other and symmetrically withrespect to the center line of the ground conductor 104.

In this case, the respective length along the length of the couplingline conductors 120 and 121 is a ¼ wavelength, i.e., ¼ λg (λg is anintra-tube wavelength), and the resonance is produced at this frequency.

Via conductors 130˜132 and via conductors 133˜135 are filled in throughholes passing through the first, second and third dielectric substrates141˜143.

The via conductors 130˜132 as shown in FIGS. 1( c) and 1(g), and the viaconductors 133˜35 as shown in FIG. 1( b), 1(c) and 1(d) short-circuitthe not-opposing end portions of the coupling line conductors 120 and121 to the ground conductors 104 and 103 at a position of the line A7–A8of FIG. 1( c) and at a position of the line A1–A2 of FIG. 1( c),respectively, thereby providing inter-digital coupling.

Since the coupling line conductors 120 and 121 have the longitudinallength of a ¼-wavelength as described above, they resonate at afrequency of the ¼ wavelength and operate as a band-pass filter at theresonance frequency.

Further, on the side surfaces of the first, second and third dielectricsubstrates 141˜143, there are formed ground conductors 105 and 106 asshown in FIGS. 1( a) and 1(b) and ground conductors 107 and 108 as shownin FIGS. 1( d)˜1(g). By enclosing the coupling line conductors 120 and121 with the ground conductors 105˜108, i.e., by using striplines, it ispossible to enhance a resistance to the electromagnetic interferencefrom outside, and place the components at higher densities, therebyminiaturizing the apparatus.

The signal input/output line conductors 112 and 113 are, as shown inFIG. 1( c), connected to the coupling line conductors 120 and 121 so asnot to be opposing each other, i.e., in a point symmetry. Theinput/output impedance is decided according to the distance from theconnection point to the end of the coupling line conductor 120 or 121.

Further, as shown in FIGS. 1( e) and 1(f), signal input/output end faceelectrodes 110 and 111 at the mounting on a printed circuit board areformed on the side surfaces of the first, second, and third dielectricsubstrates 141˜143, thereby being connected to the signal input/outputline conductors 112 and 113, respectively.

Furthermore, as shown in FIG. 1( c), via conductors 150˜163 which arefilled in through holes passing through the second dielectric substrate142 are placed on and connected to the coupling line conductor 121 asshown in FIG. 1( a), and similarly via conductors 170˜183 which arefilled in through holes passing through the second dielectric substrate142 are placed on and connected to the coupling line conductor 120 (notshown).

Here, the via conductors 150˜163 and the via conductors 170˜183 areplaced in such a manner that the via conductors 150˜163 and the viaconductors 170˜183 are close and opposing each other at regularintervals in a straight line along the longitudinal direction of thecoupling line conductors 120 and 121, as shown in FIGS. 1( a) and 1(c).

More specifically, as shown in FIG. 1( c), the via conductors 150˜163are placed along a line A9–A10 which is closer to a line intermediatebetween the two coupling line conductors 120 and 121 relative to thecenter line (line A11–A12) of the coupling line conductor 121.

That is, the via conductors 150˜163 and the via conductors 170˜183 areplaced nearer to the line intermediate between the two coupling lineconductors 120 and 121 relative to the respective center lines of thecoupling line conductors 120 and 121 along the length of the couplingline conductors 120 and 121, respectively, in a straight line uniformlyand at high densities, in such a manner that the respective viaconductors are opposing each other.

With the above-mentioned structure, it is possible to obtain the coupleras an inter-digital filter that utilizes ¼-wavelength endshort-circuited type coupling lines as shown in FIGS. 1( a)–1(g).

Next, the operation and function of the coupler that utilizes the¼-wavelength end short-circuited coupling lines, which is constructed asdescribed above, will be described.

In the case of a substrate using LTCC, since the length of the viaconductors 150˜163 and 170˜183 in the vertical direction (i.e., thethickness of the dielectric substrate) is several tens to hundredmicrons while the thickness of the coupling line conductors 120 and 121are several microns, the length of the via conductors 150˜163 and170˜183 in the vertical direction is sufficiently larger than thethickness of the coupling line conductors 120 and 121. Accordingly, byplacing the via conductors 150˜163 and 170˜183, opposing areas betweenthe coupling line conductors 120 and 121 are increased in the odd modeby an amount that is larger than an increase of the capacitance C1between the coupling line conductors 120 and 121 and the groundconductors 103˜108 in the even mode, which is expressed by [Formula 1],[Formula 2], and [Formula 4], thereby increasing the capacitance C12expressed by [Formula 1] and [Formula 4].

Therefore, as is apparent from [Formula 4], the coupler according to thefirst embodiment can increase the degree K of coupling of the couplinglines.

Further, when the opposing via conductors 150˜163 and 170˜183 are mademuch closer to each other, it is possible to obtain a higher degree ofcoupling.

As described above, according to the coupler of the first embodiment,the capacitance C12 is increased by placing and connecting the viaconductors to the coupling lines, thereby increasing the degree K ofcoupling. When this coupler is employed for a band-pass filter, it ispossible to enlarge the width of the passband, thereby realizing ahigh-density packaging of much more layers.

Further, according to the coupler of this first embodiment, by placingthe many opposing high-density via conductors as close as possible toeach other, it is possible to obtain a higher degree of coupling. Thecharacteristics of these coupling lines can be checked using an analysismethod such as a FDTD method or a finite-element method.

In this first embodiment, the coupler includes the third dielectricsubstrate 143 and the ground conductor 104, while the third dielectricsubstrate 143 and the ground conductor 104 can be eliminated to beformed by coupling lines that are composed of micro striplines.

Further, in this first embodiment, the opposing end portions of thecoupling line conductors 120 and 121 may be short-circuited to theground conductors 103 and 104 by the via conductors 130˜135, therebyproviding a comb-line coupling. In this case, it is possible to obtain acoupler, which is a comb-line filter utilizing ¼-wavelength endshort-circuited type coupling lines.

While the via conductors 130˜135 are provided in this first embodiment,it is possible to eliminate these via conductors 130˜135, and use thecoupling line conductors 120 and 121 for a directional coupler.

Further, in this first embodiment, the longitudinal length of thecoupling line conductors 120 and 121 is a ¼ wavelength, i.e., ¼ λg (λgis an intra-tube wavelength), but it is possible to make the lengthshorter than ¼ λg by attaching capacitors to open ends of the couplingline conductors 120 and 121.

Further, in this first embodiment, two coupling line conductors 120 and121 are formed symmetrically with respect to the center line of theground conductor 104, while there is no need to form these two couplingline conductors 120 and 121 in the center of the ground conductor 104.It is possible to obtain the same performance by placing these twocoupling line conductors at arbitrary positions.

EMBODIMENT 2

FIGS. 2( a)–2(g) are views illustrating a coupler that utilizes¼-wavelength end short-circuited type coupling lines according to asecond embodiment of the present invention. Components other than viaconductors 230˜232, 233˜235, 250˜261 and 270˜281 are the same as thosein the first embodiment, and their descriptions are omitted here.

FIG. 2( c) is a top plan view illustrating the coupler according to thesecond embodiment, in which parts that are not seen from the top areindicated by dashed lines. FIG. 2( a) is a longitudinal sectional viewof the coupler along line A9–A10 of FIG. 2( c), and FIG. 2( b) is alongitudinal sectional view thereof along line A11–A12 of FIG. 2( c).FIG. 2( d) is a transverse sectional view of the coupler along lineA1–A2 of FIG. 2( c), FIG. 2( e) is a transverse sectional view thereofalong line A3–A4 of FIG. 2( c), FIG. 2( f) is a transverse sectionalview thereof along line A5–A6 of FIG. 2( c), and FIG. 2( g) is atransverse sectional view thereof along line A7–A8 of FIG. 2( c).

In this second embodiment, a method of placing the via conductors250˜261 and 270˜281 on the coupling line conductors 220 and 221 isdifferent from that of the coupler according to the first embodiment.The via conductors 250˜261 and 270˜281 that are filled in through holespassing through the second dielectric substrate 242 are placed on andconnected to the two coupling line conductors 220 and 221 intermittentlyand nonuniformly so as to form thin parts and dense parts.

Here, in this second embodiment, a group of plural densely-placed viaconductors form a dense part, and such dense parts are placedintermittently to form a thin part between the dense parts.

More specifically, as shown in FIG. 2( c), among the via conductors250˜261, three via conductors, for example, 250˜252, 253˜255, 256˜258,and 259˜261 are placed densely as a group, and a large spacing isprovided between these dense parts which are the groups ofdensely-placed via conductors.

When these via conductors are placed in a longer line at high densities,it is possible to prevent cracks due to a warp that occurs in thedielectric substrate as an insulator, particularly in LTCC.

Further, as in the first embodiment, the opposing areas between thecoupling line conductors 220 and 221 are increased in the odd mode by anamount that is larger than an increase in the capacitance C1 between thecoupling line conductors 220, 221 and the ground conductors 203˜208 inthe even mode, which is expressed by [Formula 1], [Formula 2] and[Formula 4], thereby increasing the capacitance C12 expressed by[Formula 1] and [Formula 4].

Therefore, as is apparent from [Formula 4], the coupler according to thesecond embodiment can increase the degree K coupling of the couplinglines.

As described above, according to the coupler of the second embodiment,since the dense parts each being composed of a group of three viaconductors are intermittently placed on the two coupling lineconductors, the degree K of coupling of the coupling lines is increased.When this coupler is employed for a band-pass filter, it is possible toenlarge the passband, and achieve a high-density packaging of multiplelayers.

EMBODIMENT 3

FIGS. 3( a)–3(g) are diagrams illustrating a coupler that utilizes¼-wavelength end short-circuited type coupling lines according to athird embodiment of the present invention. Components other than viaconductors 330˜332, 333˜335, 350˜362, and 370˜382 are the same as thosein the first embodiment, and their descriptions are omitted here.

FIG. 3( c) is a top plan view of the coupler according to the thirdembodiment, in which parts that are not shown from the top are indicatedby dashed lines. FIG. 3( a) is a longitudinal sectional view of thecoupler along line A9–A10 of FIG. 3( c), and FIG. 3( b) is alongitudinal sectional view thereof along line A11–A12 of FIG. 3( c).FIG. 3( d) is a transverse sectional view of the coupler along lineA1–A2 of FIG. 3( c), FIG. 3( e) is a transverse sectional view thereofalong line A3–A4 of FIG. 3( c), FIG. 3( f) is a transverse sectionalview thereof along line A5–A6 of FIG. 3( c), and FIG. 3( g) is atransverse sectional view thereof along line A7–A8 of FIG. 3( c).

In the coupler according to the third embodiment, a method of placingthe via conductors 350˜362 and 370˜382 on the coupling line conductors320 and 321 is different from that in the first embodiment. The viaconductors 350˜362 and 370˜382 that are filled in through holes passingthrough the second dielectric substrate 342 are placed on and connectedto two coupling line conductors 320 and 321, respectively, so that thevia conductors are opposing each other in a zigzag manner.

According to the third embodiment, as shown in FIG. 3( c), the viaconductors 350˜362 and 370˜382 are placed on the coupling lineconductors 320 and 321, respectively, in a staggered manner, so that thevia conductors 350˜362 and 370˜382 which are respectively placed on thecoupling line conductor 320 and 321 are opposing each other.

When the via conductors are placed in the staggered manner as describedabove, it is possible to enlarge a spacing between the via conductors.When the via conductors are placed in a longer line at higher densities,it is possible to prevent cracks due to a warp that occurs on thedielectric substrate as an insulator, particularly in LTCC.

Further, since as in the first embodiment the opposing areas between thecoupling line conductors 320 and 321 are increased in the odd mode by anamount that is larger than an increase of the capacitance C1 between thecoupling line conductors 320, 321 and the ground conductors 303˜308 inthe even mode, which is expressed by [Formula 1], [Formula 2], and[Formula 4], the capacitance C12 that is expressed by [Formula 1] and[Formula 4] is increased.

Therefore, as is apparent from [Formula 4], the coupler according to thethird embodiment can increase the degree K of coupling of the couplinglines.

As described above, according to the coupler of the third embodiment, asthe via conductors are placed in a staggered manner, it is possible toenlarge the spacing between the via conductors and accordingly increasethe coupling degree K of the coupling lines. When this coupler isemployed for a band-pass filter, the passband can be enlarged, andhigh-density packaging of multiple layers can be realized.

EMBODIMENT 4

FIGS. 4( a)–4(g) are diagrams illustrating a coupler that utilizes¼-wavelength end short-circuited type coupling lines according to afourth embodiment of the present invention. Components other than viaconductors 430˜432, 433˜435, 450˜463 and 470˜483, and second lineconductors 422 and 423 are the same as those in the first embodiment,and their descriptions are omitted here.

FIG. 4( c) is a top plan view illustrating the coupler according to thefourth embodiment, in which parts that are not seen from the top areindicated by dashed lines. FIG. 4( a) is a longitudinal sectional viewof the coupler along line A9–A10 of FIG. 4( c), and FIG. 4( b) is alongitudinal sectional view thereof along line A11–A12 of FIG. 4( c).FIG. 4( d) is a transverse sectional view of the coupler along lineA1–A2 of FIG. 4( c), FIG. 4( e) is a transverse sectional view thereofalong line A3–A4 of FIG. 4( c), FIG. 4( f) is a transverse sectionalview thereof along line A5–A6 of FIG. 4( c), and FIG. 4( g) is atransverse sectional view thereof along line A7–A8 of FIG. 4( c).

In the fourth embodiment, in contrast to the first embodiment, twosecond line conductors 422 and 423 are formed between the under surfaceof the second dielectric substrate 442 and the top surface of the firstdielectric substrate 441, and the two coupling line conductors 421 and420 and the two second line conductors 422 and 423 are conducting,respectively.

Further, in this fourth embodiment, as shown in FIGS. 4( d) ˜4(g), thesecond line conductors 422 and 423 are placed between the under surfaceof the second dielectric substrate 442 and the top surface of the firstdielectric substrate 441, in parallel to the coupling line conductors420 and 421, respectively.

Further, the via conductors 450˜463 and 470˜483 that are filled inthrough holes passing through the second dielectric substrate 442 aresandwiched between and connected to the second line conductors 422, 423and the coupling line conductors 420, 421, respectively.

The via conductors 450˜463 and the via conductors 470˜483 are placed atregular intervals in such a manner that they are close to each other andopposing each other as shown in FIG. 4( c), like in the firstembodiment.

It is possible to obtain a larger spacing between the via conductors byplacing the via conductors, the coupling line conductors, and the secondline conductors in this way. Furthermore, it is possible to preventcracks due to a warp that occurs on the dielectric substrate as aninsulator by placing the via conductors in a long line at highdensities, particularly in LTCC.

Further, like in the first embodiment, since the opposing areas betweenthe coupling line conductors 420 and 421 are increased in the odd modeby an amount that is larger than an increase of the capacitance C1 inthe even mode between the coupling line conductors 420, 421 and theground conductors 403˜408, which is expressed by [Formula 1], [Formula2], and [Formula 4], the capacitance C12 that is expressed by [Formula1] and [Formula 4] is increased.

Therefore, as is apparent from [Formula 4], the coupler according to thefourth embodiment can increase the degree K of coupling of the couplinglines.

As described above, according to the coupler of the fourth embodiment,since two coupling line conductors and two second line conductors areconducting, respectively, and plural via conductors that are filled inplural through holes passing through the second dielectric substrate aresandwiched between and connected to the coupling line conductors and thesecond line conductors, it is possible to obtain a large spacing betweenthe via conductors, and thus increase the degree K of coupling of thecoupling lines. When this coupler is employed for a band-pass filter,the passband can be enlarged, and high-density packaging of multiplelayers can be realized.

EMBODIMENT 5

FIGS. 5( a)–5(g) are diagrams illustrating a coupler that utilizes¼-wavelength end short-circuited type coupling lines according to afifth embodiment of the present invention. Components other than viaconductors 530˜533, 534˜537, 550˜563 and 570˜583, and a fourthdielectric substrate 543 are the same as those in the first embodiment,and their descriptions are omitted here.

FIG. 5( c) is a top plan view illustrating the coupler according to thefifth embodiment, in which parts that are not seen from the top areindicated by dashed lines. FIG. 5( a) is a longitudinal sectional viewof the coupler along line A9–A10 of FIG. 5( c), and FIG. 5( b) is alongitudinal sectional view thereof along line A11–A12 of FIG. 5( c).FIG. 5( d) is a transverse sectional view of the coupler along lineA1–A2 of FIG. 5( c), FIG. 5( e) is a transverse sectional view thereofalong line A3–A4 of FIG. 5( c), FIG. 5( f) is a transverse sectionalview thereof along line A5–A6 of FIG. 5( c), and FIG. 5( g) is atransverse sectional view thereof along line A7–A8 of FIG. 5( c).

According to the fifth embodiment, in contrast to the first embodiment,a fourth dielectric substrate 543 having a first surface (under surface)and a second surface (top surface) which are parallel to each other isformed on the second surface of the third dielectric substrate 542, andthe ground conductor 504 is formed on the second surface of the fourthdielectric substrate 543. Then, via conductors for increasing thecoupling degree are formed in two layers, i.e., in the second and thirddielectric substrates 541 and 542, respectively.

In this fifth embodiment, as shown in FIGS. 5( a) and 5(c), viaconductors that are filled in through holes passing through the seconddielectric substrate 541 and via conductors that are filled in throughholes passing through the third dielectric substrate 542 are alternatelyplaced on and connected to the coupling line conductors 520 and 521.

That is, among the via conductors 550˜563, the via conductors 550, 552,554, 556, 558, 560 and 562 in the third dielectric substrate 542 and thevia conductors 551, 553, 555, 557, 559, 561 and 563 in the seconddielectric substrate 541 are alternately placed on the coupling lineconductor 521 along the length, as well as, among the via conductors570˜583, the via conductors 571, 573, 575, 577, 579, 581 and 583 in thethird dielectric substrate 542 and the via conductors 570, 572, 574,576, 578, 580 and 582 in the second dielectric substrate 541 arealternately placed on the coupling line conductor 520 along the length.

As the via conductors and the dielectric substrates are placed in theabove-mentioned manner, it is possible to enlarge a spacing between thevia conductors. Furthermore, when the via conductors are placed in along line at high densities, it is possible to avoid cracks due to awarp that occurs in the dielectric substrate as an insulator, especiallyin LTCC.

Further, as in the first embodiment, since the opposing areas betweenthe coupling line conductors 520 and 521 are increased in the odd modeby an amount that is larger than an increase in the capacitance C1between the coupling line conductors 520, 521 and the ground conductors503˜508 in the even mode, which is expressed by [Formula 1], [Formula2], and [Formula 4], the capacitance C12 as expressed by [Formula 1] and[Formula 4] is accordingly increased.

Therefore, as is apparent from [Formula 4], the coupler according to thefifth embodiment can increase the coupling degree K of the couplinglines.

As described above, according to the coupler of the fifth embodiment,four layers of the dielectric substrates are provided, and viaconductors are formed alternately in two layers of the second and thirddielectric substrates along the respective two coupling line conductors,whereby it is possible to enlarge the spacing between the via conductorsand thus increase the coupling degree K of the coupling lines. When thiscoupler is employed for a band-pass filter, the passband can beenlarged, and it is possible to realize a high-density packaging ofmultiple layers.

EMBODIMENT 6

FIGS. 7( a)–7(f) are diagrams illustrating a coupler that utilizes¼-wavelength end short-circuited type coupling lines according to asixth embodiment of the present invention. Here, components other thanvia dielectrics 744˜757 and 786˜799 are the same as those in the priorart of FIG. 6, and their descriptions are omitted here.

FIG. 7( b) is a top plan view illustrating the coupler according to thesixth embodiment, in which parts that are not seen from the top areindicated by dashed lines. FIG. 7( a) is a longitudinal sectional viewof the coupler along line A9–A10 of FIG. 7( b). FIG. 7( c) is atransverse sectional view of the coupler along line A1–A2 of FIG. 7( b),FIG. 7( d) is a transverse sectional view thereof along line A3–A4 ofFIG. 7( b), FIG. 7( e) is a transverse sectional view thereof along lineA5–A6 of FIG. 7( b), and FIG. 7( f) is a transverse sectional viewthereof along line A7–A8 of FIG. 7( b).

In this sixth embodiment, in contrast to the prior art, via dielectricsfor increasing the coupling degree are formed in two layers of first andsecond dielectric substrates 736 and 737, respectively.

In the sixth embodiment, as shown in FIGS. 7( a) and 7(b), viadielectrics 744˜757 and 772˜785 that are dielectrics havingpermittivities which are lower than that of the first dielectricsubstrate 736, being filled in through holes passing through the firstdielectric substrate 736, and via dielectrics 758˜771 and 786˜799 thatare dielectrics having permittivities which are lower than that of thesecond dielectric substrate 737, being filled in through holes passingthrough the second dielectric substrate 737 are placed on and connectedto the coupling line conductors 720 and 721.

Further, as in the first embodiment, the capacitance C1 between thecoupling line conductors 720, 721 and the ground conductors 703˜708,which is expressed by [Formula 1], [Formula 2], and [Formula 4], becomessmall in the even mode, while the capacitance C12 between the couplingline conductors 720 and 721 in the odd mode, which is expressed by[Formula 1] and [Formula 4], is not changed.

Therefore, as is apparent from [Formula 4], the coupler according to thesixth embodiment can increase the coupling degree K of the couplinglines.

As described above, according to the coupler of the sixth embodiment,via dielectrics that are dielectrics having permittivities which arelower than that of the dielectric substrate are filled in two layers ofthe first and second dielectric substrates along two coupling lineconductors, respectively, whereby it is possible to enhance the couplingdegree K of the coupling lines. When this coupler is employed for aband-pass filter, it is possible to enlarge the passband, and realize ahigh-density packaging of multiple layers.

INDUSTRIAL AVAILABILITY

As described above, the coupler according to the present invention issuitable for a directional coupler in a microwave circuit or a couplerthat is used for a filter, especially for a coupler that utilizesstriplines.

1. A coupler comprising: a first dielectric substrate having a firstsurface and a second surface which are parallel to each other; a seconddielectric substrate having a first surface and a second surface whichare parallel to each other, said second dielectric substrate beingplaced on said second surface of said first dielectric substrate; athird dielectric substrate having a first surface and a second surfacewhich are parallel to each other, said third dielectric substrate beingplaced on said second surface of said second dielectric substrate; aground conductor on said first surface of said first dielectricsubstrate; two coupling line conductors each having a length of a ¼wavelength, said coupling line conductors being close to each other onsaid second surface of said second dielectric substrate so as to beelectromagnetically coupled to each other; plural via conductors filledin plural through holes passing through said second dielectric substrateor said third dielectric substrate, and placed and connected to said twocoupling line conductors; and via conductors filled in through holespassing from said first dielectric substrate to said third dielectricsubstrate, and said via conductors in said through holes passing throughsaid three substrates are arranged to make opposing ends of said twocoupling line conductors short-circuit to said ground conductor on eachof said first dielectric substrate, thereby providing comb-linecoupling.
 2. The coupler as defined in claim 1, wherein said plural viaconductors filled in said plural through holes passing through saidsecond or said third dielectric substrate are via conductors filled insaid second dielectric substrate and via conductors filled in said thirddielectric substrate, which are alternately placed and connected.
 3. Thecoupler as defined in claim 2, wherein said plural via conductors filledin said plural through holes passing through said second or said thirddielectric substrate are placed and connected to said opposing twocoupling line conductors, respectively, on a part that is closer to aline intermediate between said two coupling line conductors at regularintervals in a straight line along length thereof.
 4. A couplercomprising: a first dielectric substrate having a first surface and asecond surface which are parallel to each other; a second dielectricsubstrate having a first surface and a second surface which are parallelto each other, said second dielectric substrate being placed on saidsecond surface of said first dielectric substrate; a ground conductor onsaid first surface of said first dielectric substrate; two coupling lineconductors each having a length of a ¼ wavelength, said coupling lineconductors being close to each other on said second surface of saidsecond dielectric substrate so as to be electromagnetically coupled toeach other; a third dielectric substrate having a first surface and asecond surface which are parallel to each other, said third dielectricsubstrate being placed on said second surface of said second dielectricsubstrate; a ground conductor on said second surface of said thirddielectric substrate; plural via conductors filled in plural throughholes passing through said second dielectric substrate, said viaconductors being placed and connected to said two coupling lineconductors; and via conductors filled in through holes passing from saidfirst dielectric substrate to said third dielectric substrate, and saidvia conductors filled in said through holes passing through said threesubstrates are arranged to make ends of said two coupling lineconductors, which are not opposing each other, short-circuit to saidground conductor on each of said first surface of said first dielectricsubstrate and said second surface of said third dielectric substrate,thereby providing inter-digital coupling.
 5. A coupler comprising: afirst dielectric substrate having a first surface and a second surfacewhich are parallel to each other; a second dielectric substrate having afirst surface and a second surface which are parallel to each other,said second dielectric substrate being placed on said second surface ofsaid first dielectric substrate; a ground conductor on said firstsurface of said first dielectric substrate; two coupling line conductorseach having a length of a ¼ wavelength, said coupling line conductorsbeing close to each other on said second surface of said seconddielectric substrate so as to be electromagnetically coupled to eachother; plural via conductors filled in plural through holes passingthrough said second dielectric substrate, said via conductors beingplaced and connected to said two coupling line conductors; and viaconductors filled in through holes passing from said first dielectricsubstrate to said second dielectric substrate, and said via conductorsfilled in said through holes passing through said two substrates arearranged to make ends of said two coupling line conductors, which arenot opposing each other, short-circuit to said ground conductor on saidfirst surface of said first dielectric substrate, thereby providinginter-digital coupling.
 6. The coupler as defined in claim 4 whereinsaid plural via conductors filled in said plural through holes passingthrough said second dielectric substrate are placed and connected tosaid two coupling line conductors at regular intervals.
 7. The coupleras defined in claim 4 wherein said plural via conductors filled in saidplural through holes passing through said second dielectric substrateare placed and connected to said two coupling line conductors in astraight line along a length thereof.
 8. The coupler as defined in claim4 wherein said plural via conductors filled in said plural through holespassing through said second dielectric substrate are placed andconnected to said opposing two coupling line conductors, respectively,on a part which is closer to a line intermediate between said twocoupling line conductors.
 9. The coupler as defined in claim 4 whereinsaid plural via conductors filled in said plural through holes passingthrough said second dielectric substrate are placed and connected tosaid opposing two coupling line conductors, respectively, on a partwhich is closer to a line intermediate between said two coupling lineconductors at regular intervals in a straight line along the length. 10.The coupler as defined in claim 4 wherein said plural via conductorsfilled in said plural through holes passing through said seconddielectric substrate are placed and connected to said two coupling lineconductors so as to form thin parts and dense parts.
 11. The coupler asdefined in claim 4 wherein said plural via conductors filled in saidplural through holes passing through said second dielectric substrateare placed and connected to said two coupling line conductors in such amanner that dense parts each being composed of a group of said viaconductors are placed intermittently.
 12. The coupler as defined inclaim 11 wherein said plural via conductors filled in said pluralthrough holes passing through said second dielectric substrate areplaced and connected to said opposing two coupling line conductors,respectively, on a part which is closer to a line intermediate betweensaid two coupling line conductors in a straight line along a lengththereof.
 13. The coupler as defined in claim 4, wherein said plural viaconductors filled in said plural through holes passing through saidsecond dielectric substrate are placed and connected to said twocoupling line conductors in a zigzag manner so that said via conductorsare opposing each other.
 14. The coupler as defined in claim 4 whereinsaid plural via conductors filled in said plural through holes passingthrough said second dielectric substrate are placed and connected tosaid two coupling line conductors in a staggered manner so that said viaconductors are opposing each other.
 15. The coupler as defined in claim4 further comprising: two second line conductors between said secondsurface of said first dielectric substrate and said first surface ofsaid second dielectric substrate, and said two coupling line conductorsand said two second line conductors are shaped and arranged to conductindividually, and plural via conductors filled in the plural throughholes passing through said second dielectric substrate are sandwichedbetween and connected to said coupling line conductor and said secondline conductor, respectively.
 16. The coupler as defined in claim 9further comprising: two second line conductors between said secondsurface of said first dielectric substrate and said first surface ofsaid second dielectric substrate, and said two coupling line conductorsand said two second line conductors are shaped and arranged to conductindividually, and plural via conductors filled in said plural throughholes passing through said second dielectric substrate are sandwichedbetween and connected to said coupling line conductor and said secondline conductor, respectively.
 17. A coupler comprising: a firstdielectric substrate having a first surface and a second surface whichare parallel to each other; a second dielectric substrate having a firstsurface and a second surface which are parallel to each other, saidsecond dielectric substrate being placed on said second surface of saidfirst dielectric substrate; a third dielectric substrate having a firstsurface and a second surface which are parallel to each other, saidthird dielectric substrate being placed on said second surface of saidsecond dielectric substrate; a ground conductor on said first surface ofsaid first dielectric substrate; two coupling line conductors eachhaving a length of a ¼ wavelength, said coupling line conductors beingclose to each other on said second surface of said second dielectricsubstrate so as to be electromagnetically coupled to each other; pluralvia conductors filled in plural through holes passing through saidsecond dielectric substrate or said third dielectric substrate, andplaced and connected to said two coupling line conductors; and viaconductors filled in through holes passing from said first dielectricsubstrate to said third dielectric substrate, and said via conductorsfilled in said through holes passing through said three substrates arearranged to make ends of said two coupling line conductors, which arenot opposing each other, short-circuit to said ground conductor on saidfirst surface of said first dielectric substrate, thereby providinginter-digital coupling.
 18. The coupler as defined in claim 9, saidcoupler being employed as a filter.
 19. A coupler comprising: a firstdielectric substrate having a first surface and a second surface whichare parallel to each other; a second dielectric substrate having a firstsurface and a second surface which are parallel to each other, saidsecond dielectric substrate being placed on said second surface of saidfirst dielectric substrate; a third dielectric substrate having a firstsurface and a second surface which are parallel to each other, saidthird dielectric substrate being placed on said second surface of saidsecond dielectric substrate; a ground conductor on said first surface ofsaid first dielectric substrate; two coupling line conductors eachhaving a length of a 1/4 wavelength, said coupling line conductors beingclose to each other on said second surface of said second dielectricsubstrate so as to be electromagnetically coupled to each other; pluralvia conductors filled in plural through holes passing through saidsecond dielectric substrate or said third dielectric substrate, andplaced and connected to said two coupling line conductors; and viaconductors filled in through holes passing from said first dielectricsubstrate to said third dielectric substrate, and said via conductorsfilled in said through holes passing through said three substrates arearranged to make ends of said two coupling line conductors, which arenot opposing each other, short-circuit to said ground conductor on saidfirst surface of said first dielectric substrate, thereby providinginter-digital coupling.
 20. The coupler as defined in claim 17, furthercomprising: via conductors filled in said through holes passing fromsaid first dielectric substrate to said fourth dielectric substrate, andsaid via conductors filled in said through holes passing through saidfour substrates are arranged to make ends of said two coupling lineconductors, which are not opposing each other, short-circuit to saidground conductors on said first surface of said first dielectricsubstrate and said second surface of said fourth dielectric substrate,thereby providing inter-digital coupling.
 21. The coupler as defined inclaim 18, wherein said plural via conductors filled in said pluralthrough holes passing through said second or said third dielectricsubstrate are via conductors filled in said second dielectric substrateand via conductors filled in said third dielectric substrate, which arealternately placed and connected.
 22. The coupler as defined in claim 19wherein said plural via conductors filled in said plural through holespassing through said second or said third dielectric substrate areplaced and connected to said opposing two coupling line conductors,respectively, on a part that is closer to a line intermediate betweensaid two coupling line conductors at regular intervals in a straightline along length thereof.
 23. The coupler as defined in claim 20, saidcoupler being employed as a filter.
 24. A coupler comprising: a firstdielectric substrate having a first surface and a second surface whichare parallel to each other; a ground conductor on said first surface ofsaid first dielectric substrate; two coupling line conductors eachhaving a length of a ¼ wavelength, said coupling line conductors beingclose to each other on said second surface of said first dielectricsubstrate so as to be electromagnetically coupled to each other; andplural via dielectrics having permittivities lower than that of saidfirst dielectric substrate and being filled in plural through holespassing through said first dielectric substrate, said via dielectricsbeing placed and connected to said two coupling line conductors.
 25. Thecoupler as defined in claim 23 further comprising: via conductors filledin through holes passing through said first dielectric substrate, andsaid via conductors filled in said through holes passing through saidsubstrate are arranged to make ends of said two coupling lineconductors, which are not opposing each other, short-circuit to saidground conductor on said first surface of said first dielectricsubstrate, thereby providing inter-digital coupling.
 26. The coupler asdefined in claim 23 further comprising: a second dielectric substratehaving a first surface and a second surface which are parallel to eachother, said second dielectric substrate being placed on said secondsurface of said first dielectric substrate, and a ground conductor onsaid second surface of said second dielectric substrate.
 27. The coupleras defined in claim 25 further comprising: plural via dielectrics havingpermittivities lower than that of said second dielectric substrate andbeing filled in plural through holes passing through said seconddielectric substrate, said via dielectrics being placed and connected tosaid two coupling line conductors.
 28. The coupler as defined in claim26 further comprising: via conductors filled in through holes passingthrough said first and said second dielectric substrates, and said viaconductors filled in said through holes passing through said twosubstrates are arranged to make ends of said two coupling lineconductors, which are not opposing to each other, short circuit to saidground conductors on said first surface of said first dielectricsubstrate and said second surface of said second dielectric substrate,thereby providing inter-digital coupling.
 29. A coupler comprising: afirst dielectric substrate having a first surface and a second surfacewhich are parallel to each other; a second dielectric substrate having afirst surface and a second surface which are parallel to each other,said second dielectric substrate being placed on said second surface ofsaid first dielectric substrate; a ground conductor on said firstsurface of said first dielectric substrate; two coupling line conductorseach having a length of a 1/4 wavelength, said coupling line conductorsbeing close to each other on said second surface of said seconddielectric substrate so as to be electromagnetically coupled to eachother; plural via conductors filled in plural through holes passingthrough said second dielectric substrate, said via conductors beingplaced and connected to said two coupling line conductors; and viaconductors filled in through holes passing from said first dielectricsubstrate to said second dielectric substrate, and said via conductorsfilled in said through holes passing through said two substratesshort-circuit opposing ends of said two coupling line conductors to saidground conductor on said first surface of said first dielectricsubstrate, thereby providing comb-line coupling.
 30. The coupler asdefined in claim 29, further comprising: two second line conductorsbetween said second surface of said first dielectric substrate and saidfirst surface of said second dielectric substrate, and said two couplingline conductors and said two second line conductors are shaped andarranged to conduct individually, and plural via conductors filled inthe plural through holes passing through said second dielectricsubstrate are sandwiched between and connected to said coupling lineconductor and said second line conductor, respectively.
 31. The coupleras defined in Claim 29, wherein said plural via conductors filled insaid plural through holes passing through said second dielectricsubstrate are placed and connected to said two coupling line conductorsat regular intervals.
 32. The coupler as defined in Claim 29, whereinsaid plural via conductors filled in said plural through holes passingthrough said second dielectric substrate are placed and connected tosaid two coupling line conductors in a straight line along a lengththereof.
 33. The coupler as defined in Claim 29, wherein said plural viaconductors filled in said plural through holes passing through saidsecond dielectric substrate are placed and connected to said opposingtwo coupling line conductors, respectively, on a part which is closer toa line intermediate between said two coupling line conductors.
 34. Thecoupler as defined in Claim 29, wherein said plural via conductorsfilled in said plural through holes passing through said seconddielectric substrate are placed and connected to said opposing twocoupling line conductors, respectively, on a part which is closer to aline intermediate between said two coupling line conductors at regularintervals in a straight line along the length.
 35. The coupler asdefined in Claim 29, wherein said plural via conductors filled in saidplural through holes passing through said second dielectric substrateare placed and connected to said two coupling line conductors so as toform thin parts and dense parts.
 36. The coupler as defined in Claim 29,wherein said plural via conductors filled in said plural through holespassing through said second dielectric substrate are placed andconnected to said two coupling line conductors in such a manner thatdense parts each being composed of a group of said via conductors areplaced intermittently.
 37. The coupler as defined in Claim 36, whereinsaid plural via conductors filled in said plural through holes passingthrough said second dielectric substrate are placed and connected tosaid opposing two coupling line conductors, respectively, on a partwhich is closer to a line intermediate between said two coupling lineconductors in a straight line along a length thereof.
 38. The coupler asdefined in Claim 29, wherein said plural via conductors filled in saidplural through holes passing through said second dielectric substrateare placed and connected to said two coupling line conductors in azigzag manner so that said via conductors are opposing each other. 39.The coupler as defined in Claim 29, wherein said plural via conductorsfilled in said plural through holes passing through said seconddielectric substrate are placed and connected to said two coupling lineconductors in a staggered manner so that said via conductors areopposing each other.